[FFmpeg-user] When to determine frames are progressive or interlaced ?

Andy Furniss andyqos at ukfsn.org
Wed Dec 19 21:53:54 CET 2012

tank pranav wrote:
> Hello,
> I would like to know when to determine frames are progressive or interlaced ?
> Can it be known only through the parameter "progressive sequence" which exist in "sequence extension" ?or some other fields are also need to be validated (such as top field first, progressive frames, repeat first field , etc ..... )
> or  [ is this correct that in progressive frames , there always be parameter "top field first = 0 and progressive frames = 0 and repeate first field = 0) while in interlaced frames , all above 3 parameters will contains some values ) ???
> if progressive sequence is 0 then its progressive frames.
> if progressive sequence is 1 then its its interlaced frames.
> --------------------------------------
> I have another question also regarding interlaced frames.
> IF there are two frames A and B.
> I agree if frames are interlaced then either (odd/even)  part of frame A can be part of frame B. But can it be case in which some color portion of frame B can remain present in frame A ?  (where progressive sequence is 0 and "top field first = 1).
> --------------------------------------
> It would be great if someone can answer for above questions.

I don't really understand the questions but for mpeg2 it's common for 
progressive content to say interlaced because it's been around a long 
time and a interlaced displays were common in the past.

It's common to see interlaced chroma bleed between fields as most 
software decoders will assume progressive mpeg chroma by default when 
displaying weaved frames.

mplayer has a filter ilpack which will sort this, not sure about ffmpeg.
You can also just tell mplayer that chroma is interlaced, but this is 
not as good as ilpack as it assumes 50/50 sampling IIRC, so you can get 
some artifacts from that.

If you are interested in mpeg 4:2:0 colour and interlace/progressive 
read this -


What it discusses is the case where progressive is treated as interlaced 
- so the opposite to what you will normally see on a computer. It does 
explain the general issues as well, though.

> Regards,
> Pranav.
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